The MegaĞRocketª is a heavy duty diameter caliper designed for measuring large semi-circle and round objects. The easy-to-read graphics are fractional on one side and metric on the the other. Caliper arms can be easily removed for converting from one scale to the other and quickly adjustable for zero setting to maintain accurate calibration. Graduations range from 0 to 60 inches for the fractional scale and 0 to 155cm for the metric scale. One of the unique features of the design is that only partial surfaces of objects need to be exposed to be measured. Small diameters require 180 degrees of exposure while large diameters only require 90 degrees. And, it takes all of 2Ğ3 seconds to obtain a measurement. These advantages make it a revolutionary tool useful in many different types of applications. Specifications 1.0 11 5/8" W x 26 1/2" L (1 1/2" high at knob) 2.0 Arms 3/16" tk x 1 1/4" wide aluminum powder coated. 3.0 Base plate 3/16" styrene with polycarbonate coating on both sides. 4.0 Fractional Scale: 1/4" graduations; Metric Scale: 1/2cm graduations to continuing 130cm, 1cm to 155cm. 5.0 Weight: 2lb. 2 oz.